1. Field
This invention relates to the field of tools and apparatuses used in the field of drywall construction in which panels of plasterboard are attached to wall and ceiling structures and the joints between panels are filled with compound termed mud and the compound is smoothed in preparation for sanding and finishing. The subject invention is in the particular field of tools used to spread and smooth mud on the joints between panels at an angle to each other such as at the corners of rooms and the joints between wall and ceiling panels. The tool used at such joints is known as an angle head and the specific field of the subject invention is details of the construction of an angle head.
2. Prior Art
The direct prior art to the subject invention is the type of angle head manufactured by Concorde Tool Corp. in Surrey, B.C. Canada and by Ames Taping Tool Systems, Inc. in the United States. These tools comprise two opposite hand frame assemblies, essentially rectangular, held at approximately 90.degree. to each other with one edge of one assembly touching and in accurate alignment with the similar edge of the other assembly. The assemblies are pivotally attached to a fixture such that the angle between the assemblies can change to match the angle between adjoining panels. The fixture is attached to a handle. Scraper blades are mounted in grooves near two edges of each assembly, the edges being those opposite the adjoining edges of the assemblies for the side blades, and an edge on each assembly for the top blades running from the adjoining edge on each assembly to the opposite edge, at the edges farthest from the handle of the tool in normal use condition. These two blades are termed the top blades and the accuracy of the contact of their ends at the adjoining ends of the assemblies is crucial to achieving satisfactory results with the angle head. Even a slight gap between the blade ends leaves an unacceptable ridge in the surface of the mud being smoothed by the head. The two assemblies and therefore the blades in the assemblies are held in the desired relative positions by two sheet metal clips, the top clip near the contacting ends of the top blades and the bottom clip at the lower edge of the assemblies. The function of the upper clip is most crucial. The clips are fitted into slits in the fixture to which they are attached and are made of material considerably harder than the material from which the fixture is cast. The clips engaging the grooves provide the pivotal connections of the assemblies to the fixture. Experience has shown that these clips often deform during use to the point of causing unsatisfactory performance of the head after unacceptably few hours of use. Also, the performance of the clip is unacceptably vulnerable to shock loads which can readily occur during normal use of the tool. Accordingly, the primary objective of the subject invention is to provide an angle head with more durable mechanism for holding the adjoining ends of the top scraper blades in accurate relative position and alignment.